Two things. It is absolutely monumental that Will killed Hobbs because of how Will’s mind works. Will is able to put himself in other people’s shoes; he imagines their thoughts processes—and I figure—through juxtapositioning his own life experiences over other people’s. That is how empathy works. I take the thing A that happened to me and apply it to thing B happening to you, and understand where you’re coming from. Will differs from other folks in that he’s extremely intelligent (a genius, really), knowledgeable, and sentimental. He goes into a crime scene and imagines the screams still echoing around the walls. That’s crazy (including medically). He puts himself in another man’s perspective, and extrapolates. AND he’s usually right, because he doesn’t pull shit out of thin air. He’s ALWAYS following the breadcrumbs of evidence.
Yet Will has been able to remain on the other side of the yellow tape so far because he has never killed. Because if he kills, and knew what that would FEEL like, understood how it CHANGES the killer before and after killing, then he gets TOO close to the perpetrator. He will relieve his trauma over and over and over again everytime he does his job. He will feel how it felt to kill all his life until he is dead. It will bleed into his daily life (no effective barriers), and it will ruin him. Every thought he has will be coloured by trauma.
So the fact that Hannibal makes him kill by proxy is monumental. In episode 1, Will, our main character, is already reborn. The second thing: Abigail Hobbs. Will clings to her survival because if she is able to survive Hobbs, then Will can survive Hobbs. They can overcome him together. It is desperate and shows how helpless this entire thing has made him. And then! Hannibal kills Abigail, knowing what her life means to Will. It’s morbidly poetic. Hannibal has changed Will and Will has changed Hannibal, and Hannibal is letting Will know that there is no going back anymore for either of them. All they can do is look forward, and live as the people they’ve changed into. This also connects to the Uffizi gallery scene later on and that’s just chefs kiss.